A standard phased array antenna system includes an antenna section with a plurality of antenna elements that are arranged in a two-dimensional array of rows and columns. A central waveform generator and a transmitter produce an analog signal which is to be transmitted, and this analog signal is then supplied to each of the antenna elements through respective devices that impart to the signal a respective phase shift and/or time delay. In a large array which handles wideband signals, a simple phase shift is typically not sufficient, and the capability to effect time delays must be provided.
This involves for each antenna element a relatively large and heavy analog steering section, which is expensive and consumes a significant amount of power. In fact, the steering section commonly includes long-time delay units, short-time delay units, phase shifters, and switching arrangements for routing signals among the various time delay units and phase shifters. The steering sections for different antenna elements of the same system usually need to be matched and/or calibrated, which is cumbersome and adds to the expense. These existing steering sections are also subject to dispersion that results in transmission losses and smaller available signal bandwidths. Although the discussion here is presented in the context of waveform transmission, similar considerations apply with respect to waveform reception.
Attempts have been made to develop suitable alternative approaches. One pre-existing approach involved the provision of several waveform generators and transmitters which each served a respective portion of the array, such that problems due to dispersion and transmission loss could be reduced. However, problems involving size, weight, power, cost, matching and calibration of the steering sections were still present.
Another known approach is disclosed in U.S. Ser. No. 09/478,035 filed Jan. 5, 2000, which is assigned to the same Assignee as the present application. This application disclosed an approach for processing received signals using primarily digital circuitry rather than the traditional analog circuitry. While this approach was suitable for its intended purposes, it was not satisfactory in all respects. As one aspect of this, it focused on reception and was thus advantageous for a passive system which involved only reception of signals. But in the case of an active system which needed to transmit signals, it was still necessary to provide the traditional analog steering sections with time-delay units and phase shifters, with the associated disadvantages.